The International Atomic Energy Agency (IAEA) has just said there will be no announcement until tomorrow. After a long afternoon of small group meetings and consultations with capitals, the French and the Russians returned first, and the Iranians and Americans only turned up some three hours later, at 7.30 Vienna time.

I'm told that for at least some of that missing time they have been in the office of Mohamed ElBaradei, the IAEA director general. Everyone is now back in the negotiating chamber, including ElBaradei, but making clear that there is not yet a done deal.

Officials say the finished agreement, if there is one, will look like this. Iran will export most of its stockpile of low enriched uranium to Russia. Russia would then enrich that uranium or some of its own stockpile to nearly 20% purity, and then send it to France to be turned into fuel. Then it would be sent back to Iran for the Tehran research reactor.

The key obstacles remain: 1.France's role. Iran is objecting to having France as a signatory to the deal. 2. How much of Iran's LEU will be handed over, and when?

The officials here have been unusually tight-lipped. The atmosphere is tense as there are high stakes - it would be the most substantial deal done with Iran since 2003 - and everyone is tired. But there is a general sense that a breakthrough deal could be within reach if those differences can somehow be resolved, or fudged.Update: ElBaradei emerged from the chamber to say that progress was slow, there were many technical issues involving confidence-building and guarantees, but "I believe we are making progress". "I hope we will be able to reach an agreement," he said. So not particularly upbeat by his standards. Everyone left except the Iranians and Americans. This is increasingly becoming a bilateral encounter. The Iranian ambassador, Ali Asghar Soltanieh came out smiling saying "The meeting has been constructive. We continue tomorrow."